A universal mobile telecommunication system (UMTS) is a European-type, third generation IMT-2000 mobile communication system that has evolved from a European standard known as Global System for Mobile communications (GSM).
UMTS is intended to provide an improved mobile communication service based upon a GSM core network and wideband code division multiple access (W-CDMA) wireless connection technology. In December 1998, a Third Generation Partnership Project (3GPP) was formed by the ETSI of Europe, the ARIB/TTC of Japan, the T1 of the United States, and the TTA of Korea. The 3GPP creates detailed specifications of UMTS technology. In order to achieve rapid and efficient technical development of the UMTS, five technical specification groups (TSG) have been created within the 3GPP for standardizing the UMTS by considering the independent nature of the network elements and their operations. Each TSG develops, approves, and manages the standard specification within a related region. Among these groups, the radio access network (RAN) group (TSG-RAN) develops the standards for the functions, requirements, and interface of the UMTS terrestrial radio access network (UTRAN), which is a new radio access network for supporting W-CDMA access technology in the UMTS.
FIG. 1 gives an overview of a UMTS network, including a user equipment (UE), such as a mobile station, a UMTS terrestrial radio access network (UTRAN) and a core network (CN).
The UTRAN is composed of several Radio Network Controllers (RNCs) and NodeBs which are connected via an Iub interface. Each RNC controls several NodeBs. Each NodeB controls one or several cells, where a cell is characterised by the fact that it covers a given geographical area on a given frequency. Each RNC is connected via an Iu interface to the CN, i.e. towards a Mobile-services Switching Centre entity (MSC) of the CN and a Serving GPRS Support Node entity (SGSN). RNCs can be connected to other RNCs via the Iur interface. The RNC handles the assignment and management of radio resources and operates as an access point with respect to the CN.
The NodeBs receive information sent by the physical layer of the UE through an uplink and transmit data to the UE through a downlink. The Node-Bs operate as access points of the UTRAN for the UE. The GPRS support node (SGSN) is connected via a Gf interface to an Equipment Identity Register (EIR), via a GS interface to the MSC, via a GN interface to the Gateway GPRS Support Node (GGSN) and via the GR interface to the Home Subscriber Server (HSS). The EIR hosts lists of mobiles which are allowed or are not allowed to be used on the network. The MSC which controls the connection for Circuit Switched (CS) services is connected via an NB interface towards the Media Gateway (MGW), via a F interface towards the EIR, and via a D interface towards the Home Subscriber Server (HSS). The MGW is connected via a C interface towards the HSS, and to the Public Switched Telephone Network (PSTN), and allows to adapt the codecs between the PSTN and the connected Radio Access Network (RAN).
The GGSN is connected via a GC interface to the HSS, and via a GI interface to the Internet. The GGSN is responsible for routing, charging and separation of data flows into different Radio Access Bearers (RABs). The HSS handles the subscription data of the users.
Other connections exist that are not important for the current invention.
The UTRAN constructs and maintains a radio access bearer (RAB) for communication between the UE and the CN. The CN requests end-to-end quality of service (QoS) requirements from the RAB, and the RAB supports the QoS requirements the core network has set. Accordingly, by constructing and maintaining the RAB, the UTRAN can satisfy the end-to-end QoS requirements.
The services provided to a specific UE are roughly divided into the circuit switched (CS) services and the packet switched (PS) services. For example, a general voice conversation service is a circuit switched service, while a Web browsing service via an Internet connection is classified as a packet switched (PS) service.
For supporting circuit switched services, the RNCs are connected to the mobile switching center (MSC) of the core network (CN) and the MSC is connected to the Gateway Mobile Switching Center (GMSC) that manages the connection with other networks. For supporting packet switched services, the RNCs are connected to the serving general packet radio service (GPRS) support node (SGSN) and the gateway GPRS support node (GGSN) of the core network. The SGSN supports the packet communications with the RNCs and the GGSN manages the connection with other packet switched networks, such as the Internet.
FIG. 2 illustrates a structure of a radio interface protocol between the UE and the UTRAN according to the 3GPP radio access network standards. As shown in FIG. 2, the radio interface protocol has horizontal layers comprising a physical layer, a data link layer, and a network layer, and has vertical planes comprising a user plane (U-plane) for transmitting user data and a control plane (C-plane) for transmitting control information. The user plane is a region that handles traffic information with the user, such as voice or Internet protocol (IP) packets. The control plane is a region that handles control information for an interface with a network, maintenance and management of a call, and the like. The protocol layers in FIG. 2 can be divided into a first layer (L1), a second layer (L2), and a third layer (L3) based on the three lower layers of an Open System Interconnection (OSI) standard model. The first layer (L1), namely, the physical layer, provides an information transfer service to an upper layer by using various radio transmission techniques. The physical layer is connected to an upper layer called a Medium Access Control (MAC) layer, via a transport channel.
The MAC layer and the physical layer exchange data via the transport channel. The second layer (L2) includes a MAC layer, a Radio Link Control (RLC) layer, a Broadcast/Multicast control (BMC) layer, and a Packet Data Convergence Protocol (PDCP) layer. The MAC layer handles mapping between logical channels and transport channels and provides allocation of the MAC parameters for allocation and re-allocation of radio resources. The MAC layer is connected to an upper layer called the Radio Link Control (RLC) layer, via a logical channel.
Various logical channels are provided according to the type of information transmitted. In general, a control channel is used to transmit information of the control plane and a traffic channel is used to transmit information of the user plane. A logical channel may be a common channel or a dedicated channel depending on whether the logical channel is shared. Logical channels include a Dedicated Traffic CHannel (DTCH), a Dedicated Control CHannel (DCCH), a Common Traffic CHannel (CTCH), a Common Control CHannel (CCCH), a Broadcast Control CHannel (BCCH), and a Paging Control CHannel (PCCH), or a Shared Control Channel (SCCH) and other channels. The BCCH provides information including information utilized by a UE to access a system. The PCCH is used by the UTRAN to access a UE.
For the purposes of MBMS (multimedia broadcast/multicast service; or other types of point-to-multipoint services), additional traffic and control channels are introduced in the MBMS standard. The MBMS point-to-multipoint Control Channel (MCCH) is used for transmission of MBMS control information, the MBMS point-to-multipoint Traffic Channel (MTCH) is used for transmitting MBMS service data. The MBMS Scheduling Channel (MSCH) is used to transmit scheduling information. The different logical channels that exist are listed below:

The MAC layer is connected to the physical layer by transport channels and can be divided into a MAC-b sub-layer, a MAC-d sub-layer, a MAC-c/sh sub-layer, a MAC-hs sub-layer and a MAC-m sublayer according to the type of transport channel being managed. The MAC-b sub-layer manages a BCH (Broadcast Channel), which is a transport channel handling the broadcasting of system information. The MAC-c/sh sub-layer manages a common transport channel, such as a forward access channel (FACH) or a downlink shared channel (DSCH), which is shared by a plurality of UEs, or in the uplink the Radio Access Channel (RACH). The MAC-m sublayer may handle the MBMS data.
The possible mapping between the logical channels and the transport channels from a UE perspective is given in FIG. 3.
The possible mapping between the logical channels and the transport channels from a UTRAN perspective is given in FIG. 4.
The MAC-d sub-layer manages a dedicated channel (DCH), which is a dedicated transport channel for a specific terminal. The MAC-d sublayer is located in a serving RNC (SRNC) that manages a corresponding user equipment, and one MAC-d sublayer also exists in each terminal. The RLC layer, depending of the RLC mode of operation supports reliable data transmissions and performs segmentation and concatenation on a plurality of RLC service data units (SDUs) delivered from an upper layer. When the RLC layer receives the RLC SDUs from the upper layer, the RLC layer adjusts the size of each RLC SDU in an appropriate manner based upon processing capacity and then creates data units by adding header information thereto. The data units, called protocol data units (PDUs), are transferred to the MAC layer via a logical channel. The RLC layer includes a RLC buffer for storing the RLC SDUs and/or the RLC PDUs.
The BMC layer schedules a cell broadcast (CB) message transferred from the core network and broadcasts the CB message to terminals positioned in a specific cell or cells.
The PDCP layer is located above the RLC layer. The PDCP layer is used to transmit network protocol data, such as the IPv4 or IPv6, efficiently on a radio interface with a relatively small bandwidth. For this purpose, the PDCP layer reduces unnecessary control information used in a wired network, a function called header compression.
The radio resource control (RRC) layer located at the lowest portion of the third layer (L3) is only defined in the control plane. The RRC layer controls the transport channels and the physical channels in relation to setup, reconfiguration, and the release or cancellation of the radio bearers (RBs). The RB signifies a service provided by the second layer (L2) for data transmission between the terminal and the UTRAN. In general, the set up of the RB refers to the process of stipulating the characteristics of a protocol layer and a channel required for providing a specific data service, and setting the respective detailed parameters and operation methods. Additionally the RRC handles user mobility within the RAN, and additional services, e.g. location services.
The different possibilities that exist for the mapping between the radio bearers and the transport channels for a given UE are not all possible all the time. The UE/UTRAN deduce the possible mapping depending on the UE state and the procedure that the UE/UTRAN is executing. The different states and modes are explained in more detail below, as far as they concern the present invention.
The different transport channels are mapped onto different physical channels. The configuration of the physical channels is given by RRC signalling exchanged between the RNC and the UE.
The DPCH channel can be established and used simultaneously between the UE and one or several cells of one or several NodeBs as shown in FIG. 5. This situation where the UE has a DPCH established simultaneously to several cells is called “soft handover”. The case where the UE has established a DPCH simultaneously to several cells of the same NodeB is called “softer handover”. For the DPCH the UE is always combining the TPC commands from all radio links in the downlink, and uses always the command which asks for the least transmit power (i.e. in the case one radio link says “up” and the other one “down” the UE chooses to decrease the transmit power).
The RLC layer (Radio Link Control) is a layer 2 protocol which is used in order to control the data exchange between the logical channels between the RNC and the UE. The RLC layer can currently be configured in 3 types of transfer modes:                Transparent mode,        Unacknowledged mode,        Acknowledged mode        
The detailed behaviour of these modes is described in [3]. The different functionalities that are available depend on the transfer mode.
In acknowledged and unacknowledged mode, Serving Data Units (SDUs) can be split into smaller Packet Date Units (PDUs) that are used for transmission over the air interface. The transmitter side separates the SDU into PDUs, and based on control information that is added to the PDUs the receiver side re-assembles the PDUs in order to reconstruct the SDUs. Such control information is e.g. a PDU sequence number in order to detect whether a PDU has been lost, or a Length Indicator (LI) which indicates the beginning/end of a SDU inside an RLC PDU.
In unacknowledged mode the receiver does not send a confirmation to the transmitter of correctly received PDUs, but the receiver side just reassembles PDUs to SDUs based on signalling information contained in the PDUs and transfers the complete SDUs to higher layers.
In acknowledged mode the receiver sends acknowledgements for the correctly received PDU. The transmitter uses these acknowledgements in order to initiate retransmissions of missing PDUs. The acknowledgements are sent in certain conditions. There are several mechanisms foreseen in order to initiate the transmission of the acknowledgements for PDUs received by the receiver. Which mechanisms are activated is defined in the standard and/or configured by RRC signalling. One example for such a mechanism for the transmission of a status PDU is e.g. the reception of a PDU with a sequence number that does not correspond to the latest received sequence number increased by one, or when the receiver receives an indication from the transmitter in the RLC control information that an acknowledgment (also called “Status”) should be sent. The indication of the transmitter to send a status PDU is called “Polling”.
When the transmitter sends a Polling bit a mechanism is defined in the UMTS standard if no Status report has been received after the transmission of the polling after a certain time. This mechanism initiates the transmitter to retransmit a PDU including the polling indicator and is called “timer poll”.
Another mechanism counts the number of retransmissions of a PDU. In the case the retransmission exceeds a certain number (MaxDat) the transmitter starts the reset procedure which is a procedure that allows to set the transmitter and the receiver entity of a radio bearer using AM RLC mode to an initial state. When the Reset procedure is initiated the initiating entity transmits a “Reset” PDU to the terminating entity. The terminating entity acknowledges the reception of the “Reset” PDU by transmitting the “Reset Ack” PDU. If the initiating entity has not received the “Reset Ack” PDU after a certain time the initiating entity retransmits the “Reset” PDU. If the initiating entity has not received an “Reset Ack” PDU after a certain amount of re-transmissions the initiating entity detects an “unrecoverable error”.
This disclosure describes the situation where a dysfunction is detected in the operation of a radio Link Control (RLC) entity in RLC AM mode. Other mechanisms to detect a dysfunction are already described in the UMTS standard, or possible to be imagined and implemented. It is also possible to imagine detection mechanisms for RLC entities in UM mode, which would e.g. detect that undefined signalling information is included in the RLC PDU, or where higher layers detect that the reception/transmission of the UM entity is not behaving correctly.
As explained in the above, there are mechanisms defined in the standard that detect an “unrecoverable error”, which can correspond to a blocked situation, or a situation where the communication is disturbed.
As explained in the above, there are mechanisms defined in the standard that detect an “unrecoverable error”, which can correspond to a blocked situation, or a situation where the communication is disturbed.
If the UE detects an “unrecoverable error” situation as described in the standard, the UE enters CELL_FACH state and sends a “Cell update” message to the NodeB/RNC eventually indicating that an unrecoverable error has occurred by setting the IE (Information Element) “Cell update cause” to the cause “RLC unrecoverable error”. The UE indicates by including the IE “AM_RLC error indication (RB2, RB3 or RB4)” that this unrecoverable error has either occurred for one of the Signalling Radio Bearers with the Identities 2, 3 or 4 or by including the IE “AM_RLC error indication (RB>4)” that this error has occurred for one of the Radio Bearers (RBs) using RLC AM mode with IDs higher than 4. The RNC can then send the “Cell Update Confirm” message and indicate that the RLC entities for SRBs with the IDs 2, 3 and 4, or for the RBs with Ids higher than 4 that use RLC AM mode shall be re-established by setting the IE “RLC re-establish indicator (RB2, RB3 and RB4)” and/or “RLC re-establish indicator (RB5 and upwards)” to “true”.
The UM/AM RLC entity is also responsible for handling of ciphering and deciphering. In order to do so the RLC entity in the transmitter and the receiver maintain a COUNT-C number which is composed of a Hyper fFrame nNumber (HFN) and the RLC sequence number. The COUNT-C value, together with other information is used as input to a mathematical function that generates a bitstring. This bitstring and the RLC PDU except the SN are combined by the logical XOR operation, which ensures the ciphering of the data part of the RLC PDU. The HFN value is incremented each time the RLC SN wraps around (i.e. when the RLC SN reaches its highest value and restarts from 0). In the case the receiver misses a certain number of SNs, or in the case the received SN received has been altered during the reception it is possible that the COUNT-C in the receiver and the transmitter are desynchronized. In this case the receiver is not capable to decipher correctly the information received. The receiver can detect the dysfunction of the deciphering entity by different mechanisms which are not further described here, and which are not part of the invention.
HS-DSCH is a transport channel which allows to transmit data in the downlink in the UMTS standard, and which allows to use high data rates. The HS-DSCH channel is always mapped to the HS-PDSCH physical channel. The HS-PDSCH contrary to the DPCH can only be transmitted to a given UE from one cell at a time. The HS-DSCH channel uses a hybrid ARQ mechanism which allows fast retransmission of data from the NodeB to the UE. This mechanism is also described in [2]. In order to know whether the UE has received a given block correctly, the UE sends acknowledgments to the NodeB which are sent on the HS-DPCCH physical channel in the uplink as explained in [1]. In addition, on the HS-DPCCH the UE sends the CQI information which indicates the quality of the radio channel in downlink. This allows the NodeB to adapt the transport format and the scheduling on the channel conditions.
As illustrated in FIG. 5, during the transmission in CELL_DCH the UE performs inner loop power control i.e. the UE receives transmit power commands (TPC) from the NodeB which indicate to the UE whether it should increase the transmit power or decrease the transmit power on the DCH channels as described above. The UE combines the TPC received from the different cells. Normally this means that the UE adapts the transmit power to the best radio link in the UL. The UE increases or decreases the transmit power of the DPCCH, DPDCH and HS-DPCCH. The HS-DPCCH is only received by the cell that sends the HS-DSCH. This implies that the transmit power of the HS-DSCCH DPCCH is not always adapted to the uplink channel conditions between the UE and the HS-DSCH serving cell. This means that the HS-DSCH channel can be temporarily unavailable.
One of the main advantages is that the HS-DSCH is a shared channel, which implies that the necessary spreading codes do not need to be allocated in advance and can be shared dynamically amongst different users.
The RRC mode refers to whether there exists a logical connection between the RRC of the terminal and the RRC of the UTRAN. If there is a connection, the terminal is said to be in RRC connected mode. If there is no connection, the terminal is said to be in idle mode. Because an RRC connection exists for terminals in RRC connected mode, the UTRAN can determine the existence of a particular terminal within the unit of cells, for example which cell or set of cells the RRC connected mode terminal is in, and which physical channel the UE is listening to. Thus, the terminal can be effectively controlled.
In contrast, the UTRAN cannot determine the existence of a terminal in idle mode. The existence of idle mode terminals can only be determined by the core network to be within a region that is larger than a cell, for example a location or a routing area. Therefore, the existence of idle mode terminals is determined within large regions, and, in order to receive mobile communication services such as voice or data, the idle mode terminal must moves or changes into the RRC connected mode. The possible transitions between modes and states are shown in FIG. 6.
A UE in RRC connected mode can be in different states, e.g. CELL_FACH state, CELL_PCH state, CELL_DCH state or URA_PCH state. Other states could be envisaged of course. Depending on the states the UE carries out different actions and listens to different channels. For example a UE in CELL_DCH state will triesy to listen (amongst others) to DCH type of transport channels which comprises DTCH and DCCH transport channels and which can be mapped to a certain DPCH, DPDSCH, or other physical channels. The UE in CELL_FACH state willlistens to several FACH transport channels which are mapped to a certain S-CCPCH, the UE in PCH state will listens to the PICH channel and to the PCH channel which is mapped to a certain S-CCPCH physical channel.
As described above, a radio bearer carries data from layers above the L2, i.e. data generated inside the UTRAN, e.g. RRC and Non access stratum (NAS) signalling (more generally the c-plane) and user data (the u-plane). The data from the RRC signalling is today transported via 3 signalling radio bearers, which are numbered from 0 to 2. The data from NAS signalling is transmitted on the signalling radio bearer 3 and if used 4. The remaining radio bearer identifiers are available for transmitting user plane data.
For efficient transport of the different radio bearers according to their Quality of Service (QoS) characteristics, the radio bearers can be mapped via a logical channel on different transport channels. The possible mapping options for the radio bearers depend on the type of traffic they carry. The dedicated signalling radio bearers 0-4 are mapped via a DCCH/CCCH type of logical channels. The dedicated radio bearers that carry user plane traffic with identities above 5 are mapped via DTCH type of logical channels. The possible mapping options are defined via RRC signalling. Different mapping options can be defined independently for uplink and downlink and depending on the UE state, and the transport channels that are available.
As illustrated on FIG. 7, a possible configuration for mapping options in the downlink is shown. In this example four mapping options are configured:
In CELL_DCH state when HS-PDSCH and DPCH are available the SRB#1 to #4 are mapped on the DPCH, and the other Radio Bearers RB#5 to #20 are mapped to the HS-PDSCH. The SRB#0 is not mapped in this case.
In CELL_DCH state when DPCH is available and HS-PDSCH is not available the Signalling Radio Bearers SRB#1 to #4 and the other RB#5 to #20 are mapped to DPCH. The SRB#0 is not mapped in this case. In CELL_DCH state when DPCH is not available and HS-PDSCH is available the SRB#1 to #4 and the other RB#5 to #20 are mapped to HS-PDSCH. The SRB#0 is not mapped in this case.
In CELL_FACH state SRB#0 to #4 and the other RB#5 to #20 are mapped to FACH.
In the Release 6 of UTRAN a new physical channel type is introduced which is called “fractional DPCH” and which can be used in order to replace the normal DPCH channel. This channel type reduces the number of spreading codes that are needed in the downlink by sharing one code between different users. In order to reduce the code usage, no DCH transport channel can be carried by this “fractional DPCH” physical channel, although the SRBs are mapped on the HS-DSCH.
In the uplink the SRBs and the user plane radio bearers are mapped on the DPCH, or eventually on any other available channel. This allows that the UE can transmit in the uplink.
Here are two examples of situations where Radio Link Control (RLC) entity can be affected by an error which necessitates that a Radio Network Control (RNC) entity triggers a procedure for re-initializing the Radio Link Control (RLC) entity.